Device for connecting a coaxial line to a coplanar line

ABSTRACT

The coaxial line comprises a coaxial inner conductor and a first dielectric layer encompassing the coaxial inner conductor and which is surrounded by a coaxial outer conductor. The coplanar line comprises a second dielectric layer with a coplanar inner conductor and a first and second coplanar outer conductor applied to the front side thereof and with a metallization layer followed by a substrate carrier layer on the rear side thereof. The first and second coplanar outer conductors are separated from the coplanar inner conductor by the second dielectric layer and the coaxial inner conductor is connected to the coplanar inner conductor and the coaxial outer conductor is connected to the first and second coplanar outer conductors. When high bit rate data signals are transmitted via the connecting point of the coaxial line and the coplanar line, the capacitative power is increased and undesirable reflections occur. In order to avoid this, a recess is provided in the metallization layer, beginning at the point of connection between the coaxial line and the coplanar line and extending in an approximately symmetrical manner with respect to the coplanar inner conductor, tapering in the direction of the coplanar inner conductor as the distance from the point of connection increases.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2004/052322, filed Sep. 27, 2004 and claims the benefitthereof. The International Application claims the benefits of Germanapplication No. 10345218.4 filed Sep. 29, 2003, both of the applicationsare incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The invention relates to a device for connecting a coaxial line to acoplanar line for the transmission of high bit rate data signals,wherein the coaxial line comprises a coaxial inner conductor and a firstdielectric layer encompassing the coaxial inner conductor, thedielectric layer being surrounded by a coaxial outer conductor. Thecoplanar line comprises a second dielectric layer, applied to the frontface of which are a coplanar inner conductor and a first and secondcoplanar outer conductor, and the rear face of which comprises ametallization layer followed by a substrate carrier layer. The first andsecond coplanar outer conductors are separated from the coplanar innerconductor by the second dielectric layer and the coaxial inner conductoris connected to the coplanar inner conductor and the coaxial outerconductor is connected to the first and second coplanar outerconductors.

BACKGROUND OF THE INVENTION

A simple embodiment for connecting a coaxial line, such as a coaxialplug for example, having a grounded coplanar line (“Grounded CoplanarWaveguide”, GCPW) is shown for instance in FIG. 1. The coaxial plug 1comprises a coaxial inner conductor 2, a first dielectric layer 3 and acoaxial outer conductor 4. The coplanar line 5 consists of a conductorlayer (6, 7, 8), followed by a second dielectric layer 9, ametallization layer 10 and a substrate carrier layer 11. The conductorlayer (6, 7, 8) consists of a coplanar inner conductor 6 and a first andsecond coplanar outer conductor (7, 8) which are separated from thecoplanar inner conductor 6 by the second dielectric layer 9. The coaxialinner conductor 2 of the coaxial plug 1 is connected to the coplanarinner conductor 6 of the coplanar line 5 and the coaxial outer conductor4 of the coaxial plug 1 is connected to the first and the secondcoplanar outer conductor 7, 8 of the coplanar line 5 (“earth potential”)and to the metallization layer 10 (likewise “earth potential”) that islocated on the rear face of the second dielectric layer 9. The seconddielectric layer 9 of the coplanar line 5 is usually applied over themetallization layer 10 on a metallic substrate carrier layer 11, whichserves both for mechanical stabilization and also for heat dissipationand heat distribution from components provided on the second dielectriclayer 9.

When transmitting high bit rate data signals, having a data rate ofgreater than 40 Gbit/s, for example, over the grounded coplanar line,the dispersion in the waveguide should be kept as low as possible. Thisis achieved by a tight connection of the first and second coplanar outerconductor 7, 8 to the coplanar inner conductor 6:—the width of thecoplanar inner conductor 6 is minimal, the distance between the coplanarinner conductor 6 and the coplanar outer conductors 7, 8 is short andthe thickness of the second dielectric layer 9 is also minimal.

At the point of connection between the coaxial inner conductor 2 and thecoplanar line 5, the geometry of the coaxial plug 1 requires a minimalwidth of the circumference of the coplanar inner conductor 6. This isachieved by a continuous widening of the coplanar inner conductor 6 andof the distances between the coplanar inner conductor 6 and the firstand the second coplanar outer conductors 7, 8 in the vicinity of thepoint of contact. A possible form of achieving the geometry described isshown in FIG. 2 for instance.

This widening can lead to an undesirable increase in the capacitive wireload and therefore to an undesirable local reflection, which, atfrequencies greater than 40 GHz, results in interference with thetransmission and reflection properties at the point of connection. Afurther increase in the unit-area capacitance and hence an increase inthe local reflection occurs at the point of connection between thecoaxial line and the coplanar line where the relative dielectricconstants of the first and second dielectric layer 3, 9 are different.In communication devices for the transmission of high bit rate datasignals, usually coaxial plugs 1 having a first dielectric layer 3 witha low relative dielectric constant, e.g. air (ε_(r)=1) are used and onthe other hand, for the coplanar line 5, a second dielectric layer 9with a relatively high relative dielectric constant, e.g. ceramic(ε_(r)=10) is used.

Consequently, for the transmission of high bit rate data signals,compensation of the above capacitive line load is required directly atthe point where it occurs. Compensation by means of circuitryarrangements at a different point along the transmission path, as isusual in narrow band applications, does not produce the desired effect.

For this purpose, U.S. Pat. No. 5,404,117 discloses a device forconnecting a coaxial plug to a coplanar line, wherein the capacitiveload is compensated by an inductive component. This component is made upof a free-running arrangement of the coaxial inner conductor and by aspecial indentation of the coaxial outer conductor or of a dielectricthat may possibly be present at the point of transition. Theseindentations accommodate the substrate material used for the coplanarline, yet require relatively intensive machining work and are nottherefore applicable when using commercially obtainable coaxialconnectors (such as the Anritsu V115FCPW).

Furthermore, U.S. Pat. No. 5,570,068 discloses a“Coaxial-to-Coplanar-Waveguide Transmission Line connector, in whichforming of the electric field from coaxial to coplanar is carried outwithin the coaxial line by specially machining a cavity in the coaxialouter conductor in the vicinity of the point of transition. The shape ofthis cavity accommodates the substrate material used for the coplanarline. Here, too, relatively intensive machining work is required and thearrangement can only be configured with difficulty when commerciallyobtainable coaxial connectors are being used.

SUMMARY OF THE INVENTION

The object of the invention is to provide a device for connecting acoaxial line to a coplanar line, with the aid of which, whentransmitting high bit rate data signals, the capacitive wire load thatoccurs at the point of connection between the coaxial line and thecoplanar line can be compensated with relatively little technical workbeing required. The above object is achieved, starting from a deviceaccording to the features of the claims.

The essential feature of the device according to the invention is to beconsidered as being that the metallization layer has a recess beginningat the point of connection between the coaxial plug and the coplanarline and running approximately symmetrical to the coplanar innerconductor and tapering in the direction of the coplanar inner conductoras the distance from the point of connection increases. Advantageously,the capacitive line load is compensated by a recess in the metallizationof the rear face of the coplanar line in the vicinity of the point oftransition to the coaxial line. To avoid resonances, in the designaccording to the invention, the edges of the recess run approximatelysymmetrical to the coplanar inner conductor and the recess tapers in thedirection of the coplanar inner conductor as the distance from the pointof connection increases, that is, edges of the recess that run parallelto each other are thus avoided. Particularly good resonancecharacteristics are achieved, for example, by using a triangular-shapedrecess.

In a further advantageous embodiment of the device according to theinvention, when a metallic substrate carrier layer is used, anindentation that is congruent with the recess or larger is provided inthe substrate carrier layer. Thus a short circuit in the recess isadvantageously avoided.

Further advantageous embodiments of the device according to theinvention are disclosed in the further claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereafter, embodiments of the method according to the invention aredescribed in more detail with the aid of the attached drawings.

The drawings show:

FIG. 1 a device for connecting a coaxial plug to a coplanar lineaccording to the prior art;

FIG. 2 by way of example, a diagram showing a top view onto the deviceaccording to the prior art shown in FIG. 1;

FIG. 3 by way of example, a device for connecting a coaxial plug to acoplanar line using the recess according to the invention;

FIG. 4 a section of the coplanar line that shows in more detail thegeometry of the recess in the metallization layer according to theinvention;

FIG. 5 a further embodiment of the device according to the invention bymeans of a side view of the device shown in FIG. 3 using a metallicsubstrate carrier layer;

FIG. 6 by means of a first and a second diagram, the reflection andtransmission properties at the point of transition between the coaxialplug and the coplanar line.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 shows, for instance, an embodiment of a device for connecting acoaxial line to a coplanar line, in particular for connecting a coaxialplug 1 to a coplanar line 5 for the transmission of high bit rate datasignals. The coaxial line is shown in FIG. 3 for instance by the coaxialplug 1 and comprises, in a similar manner to the embodiment shown inFIG. 1, a coaxial inner conductor 2, a first dielectric layer 3 and acoaxial outer conductor 4. The coplanar line 5 consists of a conductorlayer (6, 7, 8), followed by a second dielectric layer 9, ametallization layer 10 and a substrate carrier layer 11. The conductorlayer (6, 7, 8) consists of a coplanar inner conductor 6 and a first anda second coplanar outer conductor 7, 8, the first and second coplanarouter conductor 7, 8 being separated from the coplanar inner conductor 6by the second dielectric layer 9, for instance. The coaxial innerconductor 2 of the coaxial plug 1 is connected to the coplanar innerconductor 6 of the coplanar line 5 and the coaxial outer conductor 4 ofthe coaxial plug 1 is connected to the first and the second coplanarouter conductor 7, 8 of the coplanar line 5 and to the metallizationlayer 10 that is located on the rear face of the second dielectric layer9. In the above arrangement, the metallization layer 10 and the firstand the second coplanar outer conductor 7, 8 can be grounded. The seconddielectric layer 9 of the coplanar line 5 is applied over themetallization layer 10 on a metallic substrate carrier layer 11, in asimilar manner to that shown in FIG. 1.

To compensate for the capacitive line load that occurs when high bitrate data signals are transmitted at the connecting point between thecoaxial line or coaxial plug 1 and the coplanar line 5, a recess 12 isprovided according to the invention in the metallization layer 10. Therecess runs approximately symmetrical to the coplanar inner conductorand tapers in the direction of the coplanar inner conductor as thedistance from the point of connection increases. The thickness of therecess is equivalent to or greater than the thickness of themetallization layer 10. In the embodiment shown, the recess istriangular in shape, as a result of which a very good compensationeffect can be achieved. The width of the recess 12 at the point ofconnection between the coaxial line or coaxial plug 1 and the groundedcoplanar line 5 is approximately equivalent to the diameter of the firstdielectric layer 3 which, for instance, encompasses the coaxial innerconductor 2 in a circular manner. Furthermore, the length of the recess12 at the point of connection between the coaxial plug 1 and thegrounded coplanar line 5 along the coplanar inner conductor 6 is greaterthan the zone where the coaxial inner conductor 2 overlaps with thecoplanar inner conductor 6.

In FIG. 4, to make the geometry of the recess 12 clearer, the lower faceof the metallization layer 10 is shown separately from the substratecarrier layer 11 as an area shown with dotted lines. Additionally, theoutline of the coplanar inner conductor 6 and of the first and thesecond coplanar outer conductor 7, 8, which are arranged according tothe metallization layer 10 are indicated with the aid of dotted lines.The recess 12 is shaped like an isosceles triangle, with the apex of theisosceles triangle resting, for instance, on the central line 13 of thecoplanar inner conductor 6 in the top view.

FIG. 5 shows, in diagram form, a side view of the device depicted inFIG. 3 for connecting a coaxial plug 1 to a coplanar line 5. In contrastto the embodiment shown in FIG. 3, the substrate carrier layer 11 has,at the point of contact with the recess 12 in the metallization layer10, an indentation 14, which is rectangular, for instance. The area ofthe indentation 14 is at least congruent with that of the recess 12, sothat a short circuit can be avoided at the location of the recess 12when a metallic substrate carrier layer 11 is used. In the abovearrangement, the geometrical shape of the indentation 14 is immaterial;it is merely used for isolation at the recess 12. It is preferable,however, to use indentations 14, whose edges do not run parallel to eachother, that is, the width and/or the height of the indentation 14 in thesubstrate carrier layer 11 tapers in a direction along the coplanarinner conductor 6 as the distance from the point of connectionincreases.

FIG. 6 shows, by means of a first and a second diagram, FIG. 6 a/b, thereflection properties and transmission properties on the device shown inFIG. 3 or at the transition between the coaxial plug 1/coplanar line 5in each case with and without the recess 12. The improvement achieved inthe metallization layer 10 by using the recess 12 is clearly evident atfrequencies above 40 GHz. For instance, in the first diagram 6 a, animprovement in the reflection properties of up to 10 dB is detectable atfrequencies above 40 GHz. The transmission properties shown in thesecond diagram FIG. 6 b improve by 1 dB or more at frequencies above 40GHz.

A further advantage of the device according to the invention is thatcommercial coaxial pin-and-socket connectors can be used for theimplementation thereof, irrespective of the substrate carrier layer 11,the coplanar line 5 and of the line geometry of said coplanar line 5.

1-10. (canceled)
 11. A device for connecting a coaxial line to acoplanar line for transmission of high bit rate data signals,comprising: a coaxial line, comprising: a coaxial inner conductor, acoaxial outer conductor, a first dielectric layer encompassing thecoaxial inner conductor and surrounded by the coaxial outer conductor; acoplanar line, comprising: a coplanar inner conductor, first and secondcoplanar outer conductors which transition into a parallel course, asecond dielectric layer separating the first and second coplanar outerconductors from the coplanar inner conductor, comprising: a front facecomprising the coplanar inner conductor and the first and secondcoplanar outer conductors, a rear face comprising a metallization layerand a substrate carrier layer; a recess located at the metallizationlayer which begins at a point of connection between the coaxial line andthe coplanar line and extends along the coplanar inner conductor andtapers in a direction of the coplanar inner conductor as a distance fromthe point of connection increases, wherein the coaxial inner conductoris connected to the coplanar inner conductor and the coaxial outerconductor is connected to the first and second coplanar outerconductors.
 12. The device as claimed in claim 11, wherein the recessextends symmetrically to the coplanar inner conductor.
 13. The device asclaimed in claim 11, wherein an indentation is provided in the substratecarrier layer and is congruent with the recess at the metallizationlayer or has a greater area.
 14. The device as claimed in claim 13,wherein a width and height of the indentation in the substrate carrierlayer taper in the direction of the coplanar inner conductor as thedistance from the point of connection increases.
 15. The device asclaimed in claim 11, wherein a width of the recess at the point ofconnection between the coaxial line and the coplanar line isapproximately equivalent to a diameter of the first dielectric layerwhich circularly encompasses the coaxial inner conductor.
 16. The deviceas claimed in claim 11, wherein the recess is triangular.
 17. The deviceas claimed in claim 11, wherein a length of the recess at the point ofconnection between the coaxial line and the coplanar line along thecoplanar inner conductor is greater than a zone where the coaxial innerconductor overlaps with the coplanar inner conductor.
 18. The device asclaimed in claim 11, wherein the first dielectric layer is ambient airand the second dielectric layer is a ceramic material.
 19. The device asclaimed in claim 11, wherein the first and second coplanar outerconductors of the coplanar line are connected to an earth potential. 20.The device as claimed in claim 11, wherein the coaxial line is a coaxialplug and is connected to the coplanar line.
 21. The device as claimed inclaim 11, wherein the device is a communication device.